1. Field of the Invention
The present invention relates to a measuring apparatus for measuring an intima-media thickness of a carotid arteries, and an arterial sclerosis diagnosing system for diagnosing arterial sclerosis using the results of measurement performed by the measuring apparatus.
2. Description of the Related Art
In the past, arterial sclerosis has been diagnosed by examining a change in a vascular lumen through arteriography. However, since this method requires administration of a contrast medium or x-radiation, it cannot be implemented readily. Moreover, it takes much time for diagnosis.
In recent years, the possibility of adopting a composite thickness of the tunica intima and media, i.e., an intima-media thickness (hereinafter referred to as an "IMT") of a carotid arteries as an index of judgment of arterial sclerosis has been studied in the world. Above all, a method of imaging a carotid artery using an ultrasound system, and measuring the IMT using an ultrasonic image for the purpose of diagnosis is attracting attention.
According to the method, images of carotid arteries can be produced relatively easily. Moreover, measurement can be achieved relatively highly precisely. A measured IMT highly correlates with the one retrieved pathologically.
However, according to the foregoing conventional method, calipers are used to measure an IMT using an ultrasonic image. This poses a problem in that high-precision measurement cannot be expected unless an experienced physician carries out measurement by taking much time. Even a physician who has gotten accustomed to the measurement requires, for example, time ranging from 20 minutes to 30 minutes. Not only that it takes too much time for measurement but also the measurement is accompanied by an error dependent on the technical level of a measuring physician.
For solving the above problems, computerized methods of automatically measuring an IMT using an ultrasonic image have been proposed in some countries. However, these methods require coupling of a computer to a conventional ultrasound system. If any of the methods were implemented in an actual system, the system would be quite expensive. The prices of conventional ultrasound systems are generally as high as several tens of million yen. Any conventional ultrasound system cannot therefore be readily installed at any clinical site from the viewpoint of the price.
Moreover, a video output terminal through which an analog signal is input is generally used to capture images produced by an ultrasound system into a computer. Even when an ultrasound system reads an image as digital data, the data must be converted into an analog signal and then sent to a computer. Moreover, the computer must convert the analog video signal representing the image into digital data using video capture software or the like. According to the conventional method, therefore, deterioration in image quality cannot be avoided. This deterioration in image quality causes difficulty or errors in measuring an IMT, because measurement of an IMT requires accurate measurement in the order of 0.1 mm. Therefore, efforts must be made not to deteriorate image quality as much as possible.
In a conventional IMT measuring system based on a computer, advanced image processing is carried out in consideration of deterioration in image quality. The price of software to be installed is therefore as high as several millions yen.